Hydraulic load sensitive pressure and flow compensating system

ABSTRACT

A hydraulic load sensitive pressure and flow compensating system is provided for selectively controlling operation of a plurality of hydraulic motors. The system includes a variable delivery pump having a stroke control cylinder and supplying fluid to the motors through respective motor control valves having variable restricted flow orifices. Pressure sensitive flow dividing valves connect the control valves for delivering surplus flow from one control valve to the next in order according to priority. A pressure and flow compensating valve senses a differential pressure across the last of the control valves in the order of priority and governs the delivery of the variable delivery pump by selectively alternately applying pressure to and releasing pressure from the stroke control cylinder.

United States Patent 11 1 Young 1 Sept. 30, 1975 1 HYDRAULIC LOAD SENSITIVE PRESSURE AND FLOW COMPENSATING SYSTEM [75] Inventor: John E. G. Young, Watertown, NY.

[73] Assignee: General Signal Corporation.

Rochester, NY.

[22] Filed: Sept. 25, 1974 [21] Appl. No.: 508,977

Primary E.\aminerEdgar W. Geoghegan Attorney, Agent, or FirmHarold S. Wynn [5 7 1 ABSTRACT A hydraulic load sensitive pressure and flow compensating system is provided for selectively controlling operation of a plurality of hydraulic motors. The system includes a variable delivery pump having a stroke control cylinder and supplying fluid to the motors through respective motor control valves having variable restricted flow orifices. Pressure sensitive flow dividing valves connect the control valves for delivering surplus flow from one control valve to the next in order according to priority. A pressure and flow compensating valve senses a differential pressure across the last of the control valves in the order of priority and governs the delivery of the variable delivery pump by selectively alternately applying pressure to and releasing pressure from the stroke control cylinder.

9 Claims, 3 Drawing Figures JLP 73 Sept. 30,1975

US. Patent FIG. 1

US. Patent Sept. 30,1975 Sheet 2 Of?) 3,908,375

HYDRAULIC LOAD SENSITIVE PRESSURE AND FLOW COMPENSATING SYSTEM BACKGROUND OF THE INVENTION This invention relates to hydraulic load sensitive pressure and flow compensating systems, and while the invention is subject to a wide range of applications, it will be particularly described as a system for controlling a plurality of hydraulic motors including a variable delivery pump.

The present invention is an improvement over the hydraulic load sensitive system disclosed in a Sievenpiper application Ser. No. 393,901, filed Aug. 30, 1973, now abandoned, which is assigned to the same Assignee as the present invention and is herein incorporated by reference.

The system according to the Sievenpiper invention provides load sensitive pressure and flow compensating control for a variable delivery pump providing fluid power for operating a plurality of hydraulic motors. Fluid pressure supplied from the pump to the motors is governed by control valves having variable restricted flow orifices. A flow dividing valve is associated with each control valve for delivering surplus flow from one control valve to the next in an order according to priority. Surplus fluid flow from the flow dividing valve associated with the last of the control valves in the order of priority is applied through a restricting orifice to an atmospheric pressure reservoir. The delivery of the pump is controlled by a compensator sensing the rate of flow through the restricting orifice.

An object of the present invention is to provide a hydraulic load sensitive pressure and flow compensating system which substantially simplifies the described prior art arrangements.

Another object of the present invention is to provide a hydraulic load sensitive pressure and flow compensating system requiring a reduced number of flow dividing valves than is required according to the prior art arrangements.

Other objects, purposes and characteristic features, will be in part obvious from the accompanying drawings and in part pointed out as the description progresses.

SUMMARY OF THE INVENTION A hydraulic load sensitive pressure and flow compensating system is provided for selectively controlling operation of a plurality of hydraulic motors including a 'variable delivery pump having a stroke control cylinder and supplying fluid to the motors through respective motor control valves having variable restricted flow orifices. Pressure sensitive flow dividing valves are provided connecting the control valves for delivering surplus flow from one control valve to the next in order according to priority. A pressure compensating valve sensing a differential pressure across the last of the con- 'trol valves in the order of priority is provided for gov- For a better understanding of the present invention, together with other and further objects thereof, reference is had to the following description, taken in connection with the accompanying drawings, while its scope will be pointed out in the appending claims.

In the drawings;

FIG. 1 is a schematic drawing illustrating a hydraulic load sensitive pressure and flow compensating system as a preferred embodiment of the present invention;

FIG. 2 is a schematic longitudinal view, partly in cross section, illustrating a typical valve unit structure that can be used in the preferred embodiment of the present invention as illustrated in FIG. 1; and

FIG. 3 is a schematic longitudinal view, partly in cross section, illustrating a valve unit structure that can be used in the preferred embodiment of the present invention as illustrated in FIG. 1.

With reference to FIG. 1, a hydraulic load sensitive pressure and flow compensating system is provided for selectively controlling a plurality of operating motors or actuators typically illustrated by motors l0 and 11. The system includes a variable delivery pump 12 having a stroke control cylinder 13 and supplying fluid to the motors and 11 through respective motor control valves 14 and 15 having variable restricting orifices 16.

Pressure sensitive flow dividing valves such as valve 17 are provided for connecting the control valves for delivering surplus flow from one control valve to the next in order according to priority. Thus the valve 17 is used in delivering surplus flow from control valve 14 to control valve 15.

A pressure and flow compensating valve 18 is provided for sensing a differential pressure across the last of the control valves 15 in the order of priority. This valve governs the delivery of the variable delivery pump 12 by selectively alternately applying pressure to, and releasing pressure from, the stroke control cylinder 13.

A maximum pressure compensating valve 19 is provided for selectively connecting the pump control cylinder 13 alternately to output of the pump 12 and output to the pressure and flow compensating control valve 18.

The pump 12 and maximum pressure compensating valve 19 are combined in a pump unit 20; the control valve 14 and the flow divider valve 17 are combined in an integral valve unit 21; and the control valve 15 and the pressure and flow compensating valve 18 are combined in an integral valve unit 22.

With reference to FIG. 2, the control valve 14 has a manually operable plunger or spool 23 having an input control land 24 and exhaust control lands 25 and 26 which cooperate in a conventional manner with an input chamber 27 and exhaust chambers 28 respectively. The lands 24, 25 and 26 have variable restricting orifices 16 for manually determining the rate of flow for an associated motor 10 that is connected to control ports 29 and 30 of the control valve 14.

The flow dividing valve 17 has a valve spool 31 biased in a lefthand direction in a bore 32 in the valve unit 12 by a spring 33. The spool 31 has a control land 34 that selectively permits fluid to flow from the input chamber 27 through a chamber 35 and a surplus flow port 36. The port 36 is connected over line 37 of FIG. 1 to the input port of valve unit 22. A chamber 38 at the right of the spool 31 of the flow dividing valve 17 is subjected to pressure in control chamber 39 or control chamber 40, whichever pressure is higher, in accordance with the position of a shuttle valve 41, output of which is connected to chamber 38 through a passage 42. The left-hand end of the spool 31 is subjected to input pressure in chamber 27 by application of such pressure through an axial passageway 43 to the lefthand end of the spool 31.

A conventional relief valve 46 is provided in the valve unit 21 to protect the system in case the motor becomes stalled or reaches the end of its stroke.

With reference to FIG. 3, the valve unit 22 is similar to valve unit 21 except that the flow divider valve 17 of FIG. 2 is replaced by the pressure compensating valve 18. This valve has a spool 47 having lands 48 and 49 spaced axially by a narrow cavity 50. The lands 48 and 49 have variable restricting orifices 51 adjoining the cavity 50. The spool 47 is subject to actuation by a difference in pressure across the variable restricting orifices 16 the same as for operation of the flow dividing spool 31 (see FIG. 2) in the valve unit 21. Fluid in input chamber 27 of valve unit 22 is applied through an axial passage 52 and an orifice 53 in the spool 47 while fluid pressure on the opposite side of a restricting orifice 16 is applied to the right of the spool 47 through the shuttle valve 41 and passage 42.

A port 55 communicates with cavity 50 in the spool 47 and a passage 56 connects port 55 with the maximum pressure compensating valve 19 in pump unit 20 through a stabilizing orifice 57.

Maximum pressure compensating valve 19 has a centrally located port 60 communicating with passageway 56 extending to the valve unit 22. It has a right-hand port 61 connected by a passage 62 to output of pump 12 (see FIG. 1). Valve 19 has a spool 63 that is biased by a spring 64 in opposition to pump discharge pressure applied through port 61 to the right of a land 65. Thus spool 63 is normally in its right-hand position as shown where it provides an open passageway to connect the passageway 56 through ports 60 and 66 and passage 67 to the stroke control cylinder 13 of pump 12 (see FIG. 1).

Having thus considered the general structure of the load sensitive pressure and flow compensating system according to one embodiment of the present invention, the organization will be further considered relative to typical operating conditions.

OPERATION When the system is at rest, with the control valves 14 and on center, the pump 12 is destroked to a flow just sufficient to make up system leakage at approximately 100 p.s.i. With reference to FIG. ll, this output of pump 12 is applied over passage 62 as an input to valve unit 21, and more specifically to a pressure input port 70 of the flow divider 17. Because of control valve 14 being on center, a pilot signal is applied over pas sage 71 to compress spring 33 and cause valve 17 to divert the output of pump 12 over passage 37 to the input pressure port 72 of valve unit 22. With reference to Similarly, the control valve 15 being on center, a pilot signal is applied to passage 73 for compressing spring 74 in the pressure and flow compensating valve 18 to actuate spool 47 (see FIG. 3) and deliver fluid pressure from exhaust port 55 over passage 56 to input port of the maximum pressure compensating valve 19 in pump unit 20.

The spool 63 (see FIG. 3) of maximum pressure compensating valve 19 is in its right-hand position at this time and the land has uncovered the output port 66 to permit pilot pressure to be applied over passage 67 to the stroke control cylinder 13 (see FIG. 1) for destroking pump 12 in accordance with the pressure on flow compensating valve 18 sensing a pressure in excess of I00 p.s.i. input to valve unit 22. This compensation can be provided in valve unit 22 because this is the valve unit for the control of motor 11 that is considered to be the motor having the least priority in the succession of motor control circuits in the system. Should the pilot pressure applied to passage 73 be less than I00 p.s.i., the spool 47 (see FIG. 3) of valve 18 is moved to the left to a position to exhaust fluid from stroke control cylinder 13 of the pump 12 over passage 67, through maximum pressure compensator valve 19, over passage 56 through cavity 50 to annular exhaust chamber 75 and to an atmospheric pressure tank 76 that is common to the system. Thus the spool 47 of the pressure and flow compensating valve 18 is reciprocated in a narrow range to alternately apply pressure to and release pressure from the stroke control cylinder 13 as required to maintain the normal minimum pres sure and flow conditions which have been considered, for the purpose of illustration, to be approximately 100 psi. and 1 gallon per minute respectively. This of course maintains minimum wear on the pump 12 and minimum loss due to heating of the fluid under no load conditions.

It will now be considered that the control valve 14 is manually actuated to govern operation of the motor 10 (see FIG. 1). Actuation of this valve in either direction from its center position variably opens a passageway through a restricting orifice 16 to provide the flow desired for operation of the motor 10. Inasmuch as the valve unit 21 has its input applied at its pressure port direct from the pump 12, the motor 10 has the highest priority, and the flow dividing valve 17 adjusts itself to maintain a constant pressure across the orifice 16 such as a pressure of 100 p.s.i., and any surplus flow is delivered over passage 37 to the input pressure port 72 of valve unit 22. Drop in pressure initially applied at the input pressure port 72 of valve unit 22 is sensed by the compensating valve 18 and this valve actuates its valve spool 47 (see FIG. 3) to the left to relieve fluid pressure in stroke control cylinder 13 through chamber to the tank 76. This prints increase in output of the variable delivery pump 12 to satisfy the load that has been placed on the system, and the pressure will continue to build up until the above described normal conditions of the pressure and flow compensating valve 18 are restored.

If there are more motors to be controlled than the motors l0 and 11 illustrated in this embodiment of the present invention, it will be readily apparent that these motors may be controlled by intermediate valve units that are sequentially connected between the first priority valve unit 21 and the last priority valve unit 22, these intermediate units being substantially the same as the typical valve unit 21 that has been described. No matter how many of these intermediate valve units are operated, the valve unit 22 will be operated as has been described to govern by its compensating valve 18 fluid control of the pump 12 through the stroke control cylinder 13 to deliver pressure and flow to meet requirements of the entire system.

if the motor 11, which is the last of the motors to be controlled in the order of priority, is to be actuated, the associated control valve 15 is manually operated to govern operation of motor 11 in either direction, and such operation, the same as for motor 10, applies fluid to the motor 11 through a variable orifice 16. The spool 47 (see FIG. 3) is now positioned in accordance with a pressure differential across the orifice 16 the same as the control of spool 31 (see FIG. 2) of the flow dividing valve 17 of the valve unit 21. This will cause the spool 47 to adjust fluid applied to the stroke control cylinder 13 of the pump to a point where the differential pressure across the orifice 16 of the valve unit 22 is substantially the normal value which has been assumed to be approximately 100 p.s.i. It will be noted that although the valve 18 is controlled in a manner similar to the control of valve 17, the lands of spool 47 are different than the lands of spool 31 of flow dividing valve 17. This is because there is no flow dividing action in the pressure and flow compensating valve 18 and thus there is no surplus flow output of valve unit 21. The spool 47 is actuated within a relatively narrow range as determined by the width of the recess 50 and the size of the restricting orifices 51. The extent of reciprocal operation of spool 47 is also limited by end stops 80 and 81 that are spaced relatively short distances from the ends of the spool 47 as is illustrated in FIG. 3.

Should the load of all of the motors in the system be such as to exceed a maximum pressure setting in the maximum pressure compensating valve 19, pump discharge pressure applied through passage 62 to port 61 (see FIGS. 1 and 3) will cause spool 63 to be moved to the left to connect pump discharge pressure to the stroke control cylinder 13 and thus destroke the pump 12 to relieve the overload condition.

Having thus described a particular load sensitive pressure and flow compensating system as a preferred embodiment of the present invention, it is to be understood that various modifications and alterations may be made to the specific embodiment shown without departing from the spirit or scope of the invention.

What is claimed is:

l. A hydraulic load sensitive pressure and flow compensating sytem for selectively controlling operation of a plurality of hydraulic motors including a variable delivery pump having a stroke control cylinder and supplying fluid to the motors through respective motor control valves having variable restricting orifices .wherein the improvement comprises;

a. pressure sensitive flow dividing means connecting the control valves for delivering surplus flow from one control valve to the next in order according to priority. and

b. pressure and flow compensating valve means sensing a differential pressure across a restricting orifice of the last of the control valves in the order of priority for governing the delivery of the variable delivery pump by selectively alternately applying pressure to and releasing pressure from the stroke control cylinder.

2. A hydraulic load sensitive pressure and flow compensating system according to claim 1 wherein the pressure compensating valve means selectively connects the pump control cylinder alternately to an atmospheric reservoir and to an upstream passage of the last of the control valves in accordance with the differential pressure across the last of the control valves.

3. A hydraulic load sensitive pressure and flow compensating system according to claim 2 wherein the flow dividing means comprises a valve that delivers an access flow output in accordance with sensing a difference in upstream and downstream pressures across the restricting orifice of an associated motor control valve.

4. A hydraulic load sensitive pressure and flow compensating system according to claim 1 wherein pump output maximum pressure compensating valve means is provided for selectively connecting the pump control cylinder alternately to output of the pump and output to the pressure compensating control means.

5. A hydraulic load sensitive pressure and flow compensating system according to claim 4 wherein the maximum pressure compensating valve means is operable in response to an overload pressure output of the pump to destroke the pump.

6. A hydraulic load sensitive pressure and flow compensating system according to claim 1 wherein:

a. a first of the control valves comprises a control valve spool for governing the motor having highest priority and a flow divider valve spool disposed in respective bores of an integral valve structure, and

b. the last of the control valves comprises a control spool for governing the motor having the least priority and a pressure compensating valve spool disposed in respective bores of another integral valve Structure.

7. A hydraulic load sensitive pressure and flow compensating system according to claim 6 wherein longitudinal movement of the compensating valvespool selectively alternately applies pressure to and releases pressure from the pump control cylinder.

8. A hydraulic load sensitive pressure and flow compensating system according to claim 7 wherein longitudinal movement of the compensating valve spool selects alternately application of fluid pressure to the pump control cylinder and release of pressure from the pump control cylinder to an atmospheric pressure reservoir in accordance with reciprocation of the compensating spool.

9. A hydraulic load sensitive pressure and flow compensating system according to claim 8 wherein means is provided for reciprocating the compensating spool by variation of the differential pressure across the restricting orifice of the control valve for the motor having the least priority. 

1. A hydraulic load sensitive pressure and flow compensating sytem for selectively controlling operation of a plurality of hydraulic motors including a variable delivery pump having a stroke control cylinder and supplying fluid to the motors through respective motor control valves having variable restricting orifices wherein the improvement comprises; a. pressure sensitive flow dividing means connecting the control valves for delivering surplus flow from one control valve to the next in order according to priority, and b. pressure and flow compensating valve means sensing a differential pressure across a restricting orifice of the last of the control valves in the order of priority for governing the delivery of the variable delivery pump by selectively alternately applying pressure to and releasing pressure from the stroke control cylinder.
 2. A hydraulic load sensitive pressure and flow compensating system according to claim 1 wherein the pressure compensating valve means selectively connects the pump control cylinder alternately to an atmospheric reservoir and to an upstream passage of the last of the control valves in accordance with the differential pressure across the last of the control valves.
 3. A hydraulic load sensitive pressure and flow compensating system according to claim 2 wherein the flow dividing means comprises a valve that delivers an access flow output in accordance with sensing a difference in upstream and downstream pressures across the restricting orifice of an associated motor control valve.
 4. A hydraulic load sensitive pressure and flow compensating system according to claim 1 wherein pump output maximum pressure compensating valve means is provided for selectively connecting the pump control cylinder alternately to output of the pump and output to the pressure compensating control means.
 5. A hydraulic load sensitive pressure and flow compensating system according to claim 4 wherein the maximum pressure compensating valve means is operable in response to an overload pressure output of the pump to destroke the pump.
 6. A hydraulic load sensitive pressure and flow compensating system according to claim 1 wherein: a. a first of the control valves comprises a control valve spool for governing the motor having highest priority and a flow divider valve spool disposed in respective bores of an integral valve structure, and b. the last of the control valves comprises a control spool for governing the motor having the least priority and a pressure compensating vaLve spool disposed in respective bores of another integral valve structure.
 7. A hydraulic load sensitive pressure and flow compensating system according to claim 6 wherein longitudinal movement of the compensating valve spool selectively alternately applies pressure to and releases pressure from the pump control cylinder.
 8. A hydraulic load sensitive pressure and flow compensating system according to claim 7 wherein longitudinal movement of the compensating valve spool selects alternately application of fluid pressure to the pump control cylinder and release of pressure from the pump control cylinder to an atmospheric pressure reservoir in accordance with reciprocation of the compensating spool.
 9. A hydraulic load sensitive pressure and flow compensating system according to claim 8 wherein means is provided for reciprocating the compensating spool by variation of the differential pressure across the restricting orifice of the control valve for the motor having the least priority. 